Several of my college friends work there now. I'd be inclined to agree.

MilleniX wrote:

I think they got a lot of advantage in doing a clean-sheet design incorporating the lessons of the last several decades but not being burdened by having to depend on whichever existing NASA contractor already built that part doing it. Their operation is much more centralized both physically (4 sites in 3 states, with most of the work happening at just 1) and organizationally (only subcontracting particular components because they're the design choice, not because they get another state's legislators on board).

One of the things that really appeals to me about both of Musk's current ventures, SpaceX and Tesla Motors, is their willingness to vertically integrate manufacturing. I think there are a lot of good reasons to do so*, but a lot of companies these days are too short-sighted to make it happen.

Hell, the main concern about SpaceX is whether or not they can scale to meet their ambitious launch schedule. Two launches last year, maybe what, 5 this year, then 14 in 2014? They haven't launched any pure commercial launches in a while...

I hope they can do it, but we'll see. That's a hell of a lot more rockets than they're building now...

Hopefully they can iron out the errors that are limiting them to partial mission success If you are unable to deliver half your mission each launch like on L1 it's going to be more difficult to turn a profit as you eat insurance costs.

New milestone - the SSRMS has removed the unpressurized cargo from the Dragon's trunk (a pair of grapple fixtures for a radiator).

So Dragon has now successfully delivered both pressurized and unpressurized cargo. Pending splashdown, it looks like another successful mission for SpaceX.

Now it's a matter of seeing how well the V1.1 F9 and Merlin 1Ds perform. Given that this is SpaceX, there will be drama on the uphill climb. So far with the F9/Dragon combo, we've had an uncontrolled roll, fire on the pad from a torn umbilical, a shredded engine, and balky RCS. Wondering what's left that will be pucker-inducing without leading to LOM/LOV.

There will still be competition on the commercial payload side. Though it seems Sea Launch might be down and out for good. Once all the old Russian ICBMs are used up the floor for pricing is going to increase dramatically.

I don't think there's anyone really on the same trajectory. The closest would probably be the Chinese.

The Russians are having a hell of a time building Angara and everything else is Soviet era technology, the Europeans are having a hell of a time building Ariane 6, other parties like Sea Launch are also stuck with Soviet era tech as well. There's Orbital Sciences, but the one rocket they have that's even close to Falcon 9 uses surplus engines from the Soviet moon program (!). Other national programs don't even really aspire to commercial success. Other American companies can't get funded for anything interesting because everything has gone towards SLS, and the SLS's primary design goal was not to fix what was wrong with the Shuttle.

The Chinese are the only program that has momentum building new stuff for the commercial launch market. They're commercially significant and working hard on new stuff, though if anyone builds a fully reusable launcher I think SpaceX will beat them to it by at least a decade. If that fails, they and SpaceX will likely split the international launch market between them and someone else will fold.

Question: Who are the competitors to SpaceX, and where do they stand? I remember hearing about Carmack and Bezos both having ventures, but are they going anywhere?

With respect to NASA's commercial crew and ISS resupply efforts, the only real players in the US outside of the usual suspects (Boeing, ULA, etc.) are SpaceX, Orbital Sciences Corporation, and Sierra Nevada Corporation.

Orbital's building a new launcher (formerly Taurus II, now called Antares) and an unmanned spacecraft called the Cygnus. The Antares is due to have its maiden launch "soon" (supposedly this month).

SNC's building the Dream Chaser spacecraft, which looks like a baby Shuttle orbiter and will ride uphill on an Atlas booster. They've done at least one tethered flight test; don't know if they've done a drop test yet.

SpaceX is unique in that it's building all its own components (engines, launcher, spacecraft, etc.) in-house. Orbital is integrating bits from different vendors; the second stage is a solid motor built by ATK, and they're using Aerojet AJ-26 engines (derived from the NK-33). SNC is only building the spacecraft, relying on existing boosters to get to orbit.

Armadillo Aerospace (Carmack's company) isn't a player in commercial crew or ISS resupply. Not sure about Bezos.

Word is that the new version of the Falcon 9 will attempt to turn around using cold gas thrusters, relight the engine for a survivable reentry, and then practice landing in the ocean. The next Grasshopper version will have more realistic (eg, much weaker) legs. There was also apparently another Grasshopper flight today, we'll likely see it on Youtube soon.

It landed will a thrust to weight ratio of over 1 (eg, if it hadn't shut down the engine it would have started rising again), which is notable because the minimum thrust of one engine will be greater than the weight of a nearly empty Falcon 9 stage attempting to land. This is more efficient for physics reasons (google "gravity losses") but it basically means the production rocket will be incapable of hovering. The landing would be very difficult for a human.

I asked someone I know working on their PHD about how the computers do it, they lost me at "convex optimization".

The SpaceX term for landing under >1G acceleration is apparently "hoverslam".

-650 klbf thrust. This is a little less than RD-180, more like a third of the F-1, but 4.4x the current Merlin 1D.-Staged combustion.-Methane + Oxygen.

That last point requires a little explanation. For reasons that are too boring to get into, a methane staged combustion engine can use a fuel rich preburner while a kerosene SC engine has to be oxygen rich. That superheated oxygen is a bitch, this some extremely difficult metallurgy problems the Russians had to solve for their staged combustion kerosene engines. Methane's specific impulse is also a little higher. The specific impulse boost from methane isn't huge, but it makes staged combustion easier and the boost you get from both is significant.

My own speculation is that the relatively small size of the engine is because big pressure vessels are extremely difficult to manufacture. SpaceX would rather do something cheap to develop and cheap to manufacture than "the perfect engine" that requires a completely facility before they can even fire one. Also they need relatively small engines for their reusability technology.

My own speculation is that the relatively small size of the engine is because big pressure vessels are extremely difficult to manufacture. SpaceX would rather do something cheap to develop and cheap to manufacture than "the perfect engine" that requires a completely facility before they can even fire one. Also they need relatively small engines for their reusability technology.

This seems improbable; they could build a much larger single engine if they wanted one simply by adapting the Glushko approach of clustering combustion chambers, a la the RD-170/RD-180/RD-191 family without needing to build larger pressure chambers, although they would need new testing facilities. I would think the size chosen has more to do with the utility of an engine that size in a wide range of applications, since after all the really big Mars Colonial Transport rocket isn’t going to be built for a while and even once it is there will be plenty of payloads which won’t benefit from such a large launch vehicle being used for them. Used singly or in a small cluster of two or three, a 650K pound-force Raptor could be the basis of a reasonably sized launcher, a la the Atlas V or Falcon 9, capable of carrying payloads of maybe up to 10-25 metric tons in low orbit and reasonably sized ones into geosynchronous transfer orbits, while clustered it could be the basis of a much larger vehicle, like the Atlas V Phase II/III or the Atlas V Phase X 8.4 meter core variants which were briefly proposed for the Vision for Space Exploration before the shuttle-derived Constellation architecture was adopted, which would have carried about 100 metric tons into low Earth orbit. It does seem oversized for the upper stage role, which I had thought they were planning on using it on initially, though. But if they changed their mind on that (hardly unheard of for SpaceX), and plan on putting it in the lower stage role, then that size is a very good balance for capability in different roles.

I am curious as to where you got these numbers from, though. I cannot find any sources that mention its thrust at all, besides some (also sourceless) mentions on another forum.

Has this new engine been formally announced? I haven't seen anything on it except in discussion forums.

If you're talking about the NSF forums, they have excellent industry sources. At this point multiple people seemingly independently confirm the number, so I have pretty high confidence in it.

truth is life wrote:

This seems improbable; they could build a much larger single engine if they wanted one simply by adapting the Glushko approach of clustering combustion chambers, a la the RD-170/RD-180/RD-191 family without needing to build larger pressure chambers, although they would need new testing facilities.

What was the motivation to do that though? The Soviets never quite got the hang of extremely large numbers of engines, while SpaceX seems to be making it work. If you can handle individual engines they'll perform better and be cheaper to manufacture. A software problem.

You'll note the RD-191, which is the only recent member of the family and designed for their new Angara launcher, is single chamber. That's probably the most directly comparable engine to Raptor if the numbers can be believed.

truth is life wrote:

I would think the size chosen has more to do with the utility of an engine that size in a wide range of applications, since after all the really big Mars Colonial Transport rocket isn’t going to be built for a while and even once it is there will be plenty of payloads which won’t benefit from such a large launch vehicle being used for them. Used singly or in a small cluster of two or three, a 650K pound-force Raptor could be the basis of a reasonably sized launcher, a la the Atlas V or Falcon 9, capable of carrying payloads of maybe up to 10-25 metric tons in low orbit and reasonably sized ones into geosynchronous transfer orbits,

But they've already got that range covered with existing vehicles and the smaller engine is actually helpful for reusability.

A reusable super heavy lifter will easily accomodate any existing payload and can easily use a kick stage to reach any orbit. But it's the new markets it will create that really matter. If they were just chasing current launch contracts they could coast on the Falcon Heavy for the next 20-40 years.

truth is life wrote:

It does seem oversized for the upper stage role, which I had thought they were planning on using it on initially, though.

This seems improbable; they could build a much larger single engine if they wanted one simply by adapting the Glushko approach of clustering combustion chambers, a la the RD-170/RD-180/RD-191 family without needing to build larger pressure chambers, although they would need new testing facilities.

What was the motivation to do that though? The Soviets never quite got the hang of extremely large numbers of engines, while SpaceX seems to be making it work. If you can handle individual engines they'll perform better and be cheaper to manufacture. A software problem.

Wasn't that due to combustion instabilities in large, single chambers which made troubleshooting the design much more difficult?

If you're talking about the NSF forums, they have excellent industry sources. At this point multiple people seemingly independently confirm the number, so I have pretty high confidence in it.

That was who I was getting it from, yes. I’m quite aware of the extensive connections they have, but I can find hardly any references even there, which seems odd considering how much they discuss SpaceX.

Megalodon wrote:

What was the motivation to do that though? The Soviets never quite got the hang of extremely large numbers of engines, while SpaceX seems to be making it work. If you can handle individual engines they'll perform better and be cheaper to manufacture. A software problem.

I don’t see how this follows. A single engine in the clustered (Glushko) style will have fewer sets of turbopumps and other precision engineering equipment versus a cluster of individual engines. It’s not software issues, even if that was what doomed the N-1 in the end, it’s hardware issues; up to a point you get increased reliability from more engines because of engine-out capability, but after that the risk of catastrophic failure from any one engine on any one launch attempt starts getting excessive.

Megalodon wrote:

You'll note the RD-191, which is the only recent member of the family and designed for their new Angara launcher, is single chamber. That's probably the most directly comparable engine to Raptor if the numbers can be believed.

Well yes, obviously the RD-191 is single chamber; I specifically mentioned it. The point was that they could go the opposite direction if they wanted to to build large engines; take single-chamber engines and cluster them to form multi-chamber engines, the way Aerojet proposed/is proposing to do for the AJ-1000 (clustering two uprated NK-33/AJ-500 engines). That they do not suggests they do not want an extremely large engine.

Megalodon wrote:

But they've already got that range covered with existing vehicles and the smaller engine is actually helpful for reusability.

It’s true they have that range covered partially with existing vehicles! I specifically mentioned Falcon 9 in there, after all. However, there’s a hole in the capability range between the Falcon 9 and the Falcon Heavy, in other words between payloads that need 10 tons into LEO and those that need 50 tons. Yes, clearly those in the middle can be launched on the Heavy, but that means paying for more capability than you actually need, meaning that the customer is wasting money compared to an equally expensive (per pound) rocket better sized for a medium payload. It’s possible that SpaceX might just be so cheap that it doesn’t matter, similar to how SUVs and pickups flourished when gas was so cheap that it didn’t matter that their extra capbilities cost more money than a car better tuned to most people’s needs, but it’s quite possible they won’t be so cheap; they haven’t exactly demonstrated full commercial operation yet (flying their manifest at manifested rates). It’s also true that there aren’t a lot of commercial payloads in that range (see: the downsizing of Ariane 6), but there are government payloads (see: Delta IV Heavy), and there have been some noises from SpaceX about chasing those. Falcon 9 can cover most of them, but not all of them...a hypothetical Raptor-using rocket would be better positioned to attack that market, and possibly other nascent markets if they emerge, such as Bigelow-style turnkey space stations or commercial moon flybys or what not.

Moreover, and more importantly from my point of view, by designing a rocket using these Raptors as sea-level engines, they would reap the benefits of commonality with their larger MCT, which is going to be massively oversized for launching commercial (ie., paying) payloads at anytime in the next decade or two, in much the same way that by having the Merlin 1D and Merlin Vacuum they can reap internal commonality between their lower and upper stages. By having only a few engine designs, they need to maintain fewer production lines, saving them money...an important consideration, because the MCT is going to be a money sink for a long while.

And I don’t dispute that having a lower base thrust helps with reusability; as we agreed on the other thread, there are practical limits to how low you can throttle, throttling is an expensive capability, and so (given that rockets tend to be much lighter coming down than going up) all else being equal for a VTVL reusable rocket you’d rather have a cluster of small engines rather than a single large engines. This 650K pound-force engine still seems small enough that, particularly if they accept a T/W > 1 on landing like they are with Falcon 9, they could use it as a landing engine.

Megalodon wrote:

A reusable super heavy lifter will easily accomodate any existing payload and can easily use a kick stage to reach any orbit. But it's the new markets it will create that really matter. If they were just chasing current launch contracts they could coast on the Falcon Heavy for the next 20-40 years.

It can lift basically any payload to any orbit, true, by virtue of being grossly oversized for any existing payload, which brings up the problem I mentioned earlier of the Falcon Heavy being oversized for the comsat (for instance) market in spades. This time, there's not a question; it's simply going to be too expensive for existing payloads to use in any reasonable way. The MCT is basically a 747 when the biggest payloads around are DC-3-sized. I know Elon Musk wants to do it to send people to Mars, and that’s fine, it’s his own money, but the MCT isn’t going to be making SpaceX any money at all any time soon. Why would anyone want to use it, especially when they could launch their payloads on reusable Falcon 9/Falcon Heavy, which would be cheaper and just as capable of putting their stuff up where they want it?

As for “new markets it will create”...well, I remember the Shuttle. I’ll believe it when I see it.

Megalodon wrote:

It's not oversized if the first stage is proportionately bigger.

Making a proportionately bigger first stage doesn’t make any financial sense. I know Elon really really wants it to happen, and it’s his company so it’s probably going to happen anyways, but he’s getting ahead of himself there.

However, there’s a hole in the capability range between the Falcon 9 and the Falcon Heavy, in other words between payloads that need 10 tons into LEO and those that need 50 tons. Yes, clearly those in the middle can be launched on the Heavy, but that means paying for more capability than you actually need, meaning that the customer is wasting money compared to an equally expensive (per pound) rocket better sized for a medium payload.

Don't overlook the possibility of multiple payloads per launch into LEO or GPS-like orbit altitudes as a means of reducing the cost per ride on a Heavy.

Don't overlook the possibility of multiple payloads per launch into LEO or GPS-like orbit altitudes as a means of reducing the cost per ride on a Heavy.

Oh, I haven’t. The problem with multi-manifesting, though, is that it requires either a customer with multiple satellites who’s willing to let them all launch together (remember, this increases the risk from a single launch failure) or multiple customers whose payloads have sufficiently common launch requirements that they can share a ride (and who are willing to share a ride, of course), neither of which is especially easy to find, particularly as you increase the number of satellites you need to launch simultaneously to “fill up”. There’s also the problem of the (slow) growth in satellite sizes, which causes a (slow) reduction in the number of satellites which can be simultaneously manifested. The Ariane IV started off being able to (and routinely being) dual-manifest, but nowadays even the heaviest version could only launch one satellite. Similarly, even the Ariane V nowadays is a bit undersized for dual-manifesting the latest and greatest GTO communications satellites (which are where the $$$ are presently), part of the reason they’re doing the Ariane V ME upgrade with the restartable Vinci engine (which will increase performance).

But you see the Ariane VI, well, it’s going to be smaller than the Ariane V. About the size of the Falcon 9, as a matter of fact. And it will be single-manifesting. Partially this is from political requirements that SpaceX doesn’t face, but they felt that a large, multi-manifesting rocket would make no financial sense--it would be too expensive per launch, even so--and they didn’t have any government payloads that would fill up a larger, Ariane V-sized rocket (the Ariane V itself was built around Hermes, which would have needed every bit of its capability...but which was never actually built). I suspect the same is going to be true for SpaceX, the Falcon 9 will get all the customers, the Falcon Heavy the occasional one-offs that really need the big capacity.

That was who I was getting it from, yes. I’m quite aware of the extensive connections they have, but I can find hardly any references even there, which seems odd considering how much they discuss SpaceX.

I've seen multiple, apparently independent reports of that number. Some are in the paid section. I'm pretty confident it reflects current plans.

truth is life wrote:

A single engine in the clustered (Glushko) style will have fewer sets of turbopumps and other precision engineering equipment versus a cluster of individual engines.

I think much of SpaceX's work has been to bring a lot of this in house with all kinds of 3D printers and CNC machines, versus a lot of these older engines that have a lot of hand machined parts. I am virtually certain that SpaceX has the cheapest thrust around, in spite of the fact that they need 9 engines to do what most others do with 1. Clustered combustion chambers need manifolds that have to deal with much higher temperature and pressure than fuel plumbing does. That's not free either.

truth is life wrote:

Moreover, and more importantly from my point of view, by designing a rocket using these Raptors as sea-level engines, they would reap the benefits of commonality with their larger MCT, which is going to be massively oversized for launching commercial (ie., paying) payloads at anytime in the next decade or two, in much the same way that by having the Merlin 1D and Merlin Vacuum they can reap internal commonality between their lower and upper stages. By having only a few engine designs, they need to maintain fewer production lines, saving them money...an important consideration, because the MCT is going to be a money sink for a long while.

Flip that on its head. If you think about the likely size of an MCT using these engines on both stages, it'll probably be at least in SLS territory when expendable, and at least in Falcon Heavy territory when reusable. It would easily accomodate any existing payload, and when reusable, the surplus payload will matter even less than it already does. But will also easily accomodate any space station/moon/mars plans anyone might have.

I get the impulse to assume mundane outcomes, and I agree SpaceX's probability of success is nowhere near certainty, but it is extremely hard to reconcile this with Musk's goals. What you propose is a bad use of resources and does not advance goals that matter to him. Moreover no such mid range vehicle is even rumored at this point, this idea is imposed ad hoc on the rumors/leaks of a mid level thrust engine. It's what other people might do with an engine like that. The only new engine we know about is Raptor, and Musk has said that's the only one they're working on. The only new vehicle we know about is MCT. As far as Musk is concerned, the existing launch market has already been checkmated, and he's now using the company he's built to advance the larger goals.

truth is life wrote:

It can lift basically any payload to any orbit, true, by virtue of being grossly oversized for any existing payload, which brings up the problem I mentioned earlier of the Falcon Heavy being oversized for the comsat (for instance) market in spades.

I am profoundly confused as to why a customer might respond to the prospect of their satellite being too small for the $85m launch but too big for the $55m launch by being ridden with angst that they're not going to use the entire capacity of the $85m launcher.

So what?

Ballast the fucker and be done with it if you don't want to dual manifest. You'll do it and you'll like it because you won't do better anywhere else. The entire commercial market doesn't justify endless variants in the midrange. SpaceX could poach every launch contract in the world and not get there.

truth is life wrote:

As for “new markets it will create”...well, I remember the Shuttle. I’ll believe it when I see it.

As will I. But Musk is committed to it. Committed in context doesn't mean certain of success, but rather defining anything less as failure. There's no point to this exercise as far as he's concerned if it doesn't lead to the goal of a large scale presence in space.

So this had previously been rumored, but was confirmed by Musk in the CRS-2 conference call:

The next version of Falcon 9 will be designed to do a velocity reduction burn so it can survive reentry. It will then do another burn immediately prior to splashdown. The stage might not be reusable, but they should be able to at least recover and inspect it. Musk says they plan to attempt return to launch site with landing as early as middle of next year, though this is obviously subject to revision. He made a point of saying they expect this to require multiple attempts.

If successful, this would be the first recovery of a mostly intact liquid first stage from an orbital launch that I am aware of. The Shuttle obviously had recoverable SRBs, but those were built like a brick shithouse.

One comment on the Raptor engine. SpaceX currently uses their Merlin w/ a modified nozzle for vacuum on their second stage. A LOX-Methane engine has better efficiency (Isp for you rocket folks) than the Merlin (LOX-RP1), but not as much as a LOX-LH2. Most other rockets use LOX-LH2 for their upper stage because of its performance, but the penalty is that LH2 requires tankage that can maintain ~20K temperature (STP) to remain liquid... which has penalties. Methane, on the other hand, boils at 109K (again, STP) - so the insulation requirements are much less. Insulation is basically dead weight, so less is better and heat transfer is a non-linear problem.

Given that SpaceX has taken the approach of 'best performance for the money' rather than 'best performance we can get' I'm confident they considered the impacts of tankage and other items when deciding that LOX-Methane was the right choice for a high performance stage 2+.

Of course LOX-Methane engines have little to no heritage in space applications; its also new territory. Or at least new territory for an operational system. Its a big step for SpaceX. Not to belittle their accomplishments (seriously, they are doing outstanding work), but from an engineering/technology perspective they haven't done anything new yet. What SpaceX has done is apply a different business model to the technology/industry and (so far) prove that there is a better approach to getting mass to orbit. The Raptor engine and Grasshooper are departures from 'done before, lets do better' and that's huge, both in terms of risk and reward.

(New comment because its a different topic)With regards to creating 'new markets' and the Falcon Heavy, there is some logic to Musk's 'If we build it they will come' mentality. The history of satellites show that they will grow to meet their launch vehicle size. In the realm of comm sats, basic physics says that to increase power (and thus SNR) at the receiver, you either use more broadcast power (bigger solar panels), have a bigger transmitter antenna (more gain), or have a bigger receiver antenna (more gain). 2 of the 3 translate to bigger satellites. Moreover, bigger ground antennas aren't always possible - ex. a home satellite dish. There are deployable reflectors (ex. Thurya) but they present other challenges.

A simple example - DirecTV (or Dish) receivers are 1ftx1.5ft ellipse. If you double the broadcast power (either 2x gain, 2x power, or some mix) the receiver dish could shrink to 6in diameter, or the size of a small plate. Drive it up even more and the antenna can be even smaller, or more realistically change to a simple antenna like a flat roof patch antenna instead of a precision parabolic antenna.

Historically, as bigger launch vehicles became available, satellites grew. If (and its a big if) SpaceX can provide the throw weight at the cost they plan then companies like Boeing, LM, NGC, ATK (don't know the European companies but insert them here) will build bigger satellites to take advantage of them. Additionally, dual manifesting for GEO is stupid-easy from an orbital mechanics perspective - so companies like Intelsat & SES Americom can save a lot of money (at some risk) by multi-manifesting on a single launch. There are risks to a single-launch, but that's why companies buy insurance.

One comment on the Raptor engine. SpaceX currently uses their Merlin w/ a modified nozzle for vacuum on their second stage. A LOX-Methane engine has better efficiency (Isp for you rocket folks) than the Merlin (LOX-RP1), but not as much as a LOX-LH2. Most other rockets use LOX-LH2 for their upper stage because of its performance, but the penalty is that LH2 requires tankage that can maintain ~20K temperature (STP) to remain liquid... which has penalties. Methane, on the other hand, boils at 109K (again, STP) - so the insulation requirements are much less. Insulation is basically dead weight, so less is better and heat transfer is a non-linear problem.

Well put.

Hydrogen also has very low density which has knock on effects (bigger tanks so insulation is even worse, engines are less powerful).

Methane's boiling point is higher than Oxygen's, and we deal with it all the time as LNG.

longhornchris04 wrote:

Not to belittle their accomplishments (seriously, they are doing outstanding work), but from an engineering/technology perspective they haven't done anything new yet.

If they recover the first stage I'm pretty sure that'll be a first for a liquid fueled rocket. They'll be attempting that on their next few flights.

Sorry, Standard Temperature and Pressure - i.e. normal atmospheric temp and pressure... which now I think about it makes little sense.

What I meant to say was that at normal atmospheric pressure H2 must be kept much colder than O2 or CH4. Most spacecraft tanks operate above atmospheric pressure, but higher pressures come with the mass penalty of heavier tankage. There's an engineering trade between tank pressure, tank insulation, and other operational needs like maintaining the flow rate.

Given how SpaceX has approached things so far, I expect they determined that CH4 offered a better cost to performance ratio for an upper stage engine compared to H2. Furthermore, it allows them to apply their existing LOX cryogenic technology which can maintain <~90K (at atmospheric pressure) to store Liquid Methane at <109K (again, atmo pressure). That alone may have made the trade decision.

Finally, there's still the 'hope' that we can manufacture methane on Mars. Elon has stated that his goal is Mars, so this is another step along that path.

Sorry, Standard Temperature and Pressure - i.e. normal atmospheric temp and pressure... which now I think about it makes little sense.

What I meant to say was that at normal atmospheric pressure H2 must be kept much colder than O2 or CH4. Most spacecraft tanks operate above atmospheric pressure, but higher pressures come with the mass penalty of heavier tankage. There's an engineering trade between tank pressure, tank insulation, and other operational needs like maintaining the flow rate.

Given how SpaceX has approached things so far, I expect they determined that CH4 offered a better cost to performance ratio for an upper stage engine compared to H2. Furthermore, it allows them to apply their existing LOX cryogenic technology which can maintain <~90K (at atmospheric pressure) to store Liquid Methane at <109K (again, atmo pressure). That alone may have made the trade decision.

Finally, there's still the 'hope' that we can manufacture methane on Mars. Elon has stated that his goal is Mars, so this is another step along that path.

Another advantage is that Methane is much easier to store in orbit for long periods of time. Hydrogen would not be insurmountable and boiloff could be kept extremely low with proper care, but basically it's very difficult to design a solution that works indefinitely in low Earth orbit, and this would be much easier for Methane.

A BotE estimate for the SSTO performance for an engine the size of the rumored Raptor from the Mars surface would be about 20 metric tons. That seems reasonable or even high for crew return with samples.

Another advantage is that Methane is much easier to store in orbit for long periods of time. Hydrogen would not be insurmountable and boiloff could be kept extremely low with proper care, but basically it's very difficult to design a solution that works indefinitely in low Earth orbit, and this would be much easier for Methane.

Right. Hydrogen boils at 1 atm at just 14.1 K. The background of space is 2.7 K, and in high orbit you can you cool a tank down to liquid hydrogen storage temperatures with just a multi-layer reflective sunshade. In low Earth orbit, however, you've got the Earth covering half the sky and radiating at ~300 K, and the direction of the Earth and sun are always changing. The simple sun-shade approach doesn't work in low orbit, you need active cooling, which takes power and has mechanical parts to wear out.

Methane stays liquid below 113 K at 1 atm, it's easier to store than liquid oxygen (90.2 K). And methane also forms a clathrate ice with water that's stable at around the freezing point of water and moderate pressure. This isn't practical for transport (unless you need to ship lots of water anyway) or fuel because the water far outmasses the methane, but it could be useful for storage in locations where cooling costs of liquid methane would be excessive...say a lunar or martian surface base.

Somewhat of a different approach to Falcon 9, but significantly lower risk for NASA so I think it was a good call. They have two new domestic launch vehicles and two spacecraft for significantly less than anything else in the US would cost.

It's assembled from pretty well established technology, including extremely high performance Russian engines. Aerojet has a license to manufacture new ones once the stock from Russia runs out. The upper stage is a solid booster, which is atypical, and there's a coast phase between the stages which is also atypical, but there's a lot less risk associated with that approach. That first stage is just such a champ with those Russian staged combustion engines that it doesn't need a high energy upper stage to reach LEO, and there's a huge upgrade path now for the upper stage. With a higher energy upper stage this is a great Delta II class launcher for interplanetary missions.

The Cygnus spacecraft is also a different take from SpaceX. Their pressurized volume is immensely larger than Dragon's, and on the Falcon 9 v1.1 Dragon will be volume limited, not mass limited. Orbital is a contractor for many commercial satellites so they have enormous experience in this area. On the flipside, Cygnus is not capable of surviving reentry, but that's mostly ok. All the other available cargo craft like Russia's Progress and the European ATV reenter destructively for garbage disposal.

This is pretty great news all around. Two completely independent launch platforms, with some complementary strengths, both at much lower cost than their predecessors. I'm especially glad to see way less drama on this flight than SpaceX had in their initial tests.

The design is now validated, but the manufacturing thing still seems like a risk to me - has Aerojet established that they can properly reproduce the designs that they're currently refurbishing? I almost feel like they'll have to re-validate on some dummy payloads when they make the transition, since stand-firing can't pick up systems engineering or integration flaws that may have been introduced.

The solid component seems a bit odd to me. As many have remarked, it makes success through the second stage much closer to all or nothing. It's got some thrust vectoring, so at least some trajectory flaws could still be corrected at that point, but the burn-time is completely fixed. Then again, the first stage has two engines, so one going out is an instant mission failure anyway.

The design is now validated, but the manufacturing thing still seems like a risk to me - has Aerojet established that they can properly reproduce the designs that they're currently refurbishing?

I would venture yes. If you look at the Ars article on the F1 and how they designed it with extremely high margins so manufacturing defects wouldn't be fatal, I doubt a Soviet engine from the same era would be any less tolerant. The tricky bit that's had westerners stumped is the metallurgy for the Oxygen rich preburner, if they've licensed that then I think it'll be ok.

I think it's just the simplest and cheapest way for Orbital to complete an orbital launcher. The solid second stage is something they get from ATK. Upgrading that is available as an option if there's customers for it, but I agree with the philosophy of not making "awesome" a dependency for "works".

Another possible reason for shifting to LOX/Methane engines is discussed in The Case for Mars. Basically the author worked on a prototype device to create methane from imported H2 and atmospheric gasses on Mars. One of the biggest technical issues raised was a lack of LOX/Methane propulsion. Those two components equaled a low cost there and back again Mars mission. Musk has already made his interest in Mars a headline event. This seams to be laying groundwork.